Line widths of patterns in the semiconductor device are generally reduced to increase the density of those devices. There are, however, practical limitations to increasing the design of devices. For example, in the fabrication of DRAM devices, the formation of an active pattern may include the steps of forming a preliminary mask pattern shaped like a line, dividing the preliminary mask pattern into a plurality of mask patterns using a trim process, and then, etching a substrate using the mask patterns as an etch mask to form a trench defining the active patterns.